# General Class License Theory II. Dick Grote K6PBF

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1 General Class License Theory II Dick Grote K6PBF 1

2 Introduction In the first theory class we talked about basic electrical principles and components. Now we will build on this to learn about Practical Circuits Signals and Emissions 2

3 Rectifiers and Power Supplies Nearly all electronics runs on DC voltage. Need to convert AC house voltage (117 or 220V) to DC voltages almost always at different voltage levels. Useful components to effect this: Transformers to change AC voltage levels Diode(s) to convert AC to DC Capacitors to store energy and smooth out waveforms 3

4 Half Wave Rectifier AC Input V P V OUT V OUT E RMS V = V OUT V AVE = RMS V P V =.45V RMS Diode 1.41 V Diode Current flows through the diode during 180 of AC c ycle. 4

5 Half Wave Rectifier Peak Inverse Voltage V OUT AC Input V P V OUT E RMS If we were to put a capacitor across the output of this rectifier then the output voltage would charge up to V P. We can then see that during the negative half cycle: Peak-inverse voltage across the half wave rectifier (e.g. diode) is two times the peak of the output voltage. 5

6 Full Wave Rectifier AC Input V P V P V V OUT = V AVE RMS = 2 V P 2.8 V =.9 V V RMS Diode Diode Center tapped transformer allows currents to flow alternately through 2 diodes so current flows 360 of AC cycle. Pulses through load are a series of pulses at twice the frequency of the input. 6

7 Full Wave Bridge Rectifier Bridge Rectifier: AC Input Eliminates the need for a tapped transformer at the expense of 2 additional diodes Peak-inverse voltage across rectifiers in a full wave bridge rectifier is equal to the normal peak (Vp) of output voltage of power supply. 7

8 Power Supply Filters Rectifier Bleeder V LOAD Capacitors and inductors are used in power supply filter networks? Filter smoothes pulses so that V LOAD approximates DC voltage Capacitor choices are important because they are constantly charging and discharging. It is important internal resistance of C s (termed ESR or Equivalent Series Resistance) is low. The Bleeder resistor ensures that discharges the filter capacitors are discharged when the power is removed. 8

9 Switch-Mode Power Supplies A Switch-mode power supply uses a switching regulator operating at a higher frequency to control the conversion of electrical power in a highly efficient manner. Usually are they are called switching power supply. The advantage of switching power supply compared to linear power supplies is high frequency operation allows the use of smaller components. 9

10 Schematic symbols During this presentation several schematic symbols have been introduced. The ARRL has a page full of them in their material. These are the ones you will need to know: Voltage Controlled Capacitor Zener diode Multiple-winding transformer NPN bipolar transistor Tapped inductor FET 10

11 Digital Circuits Digital circuits operate in only of two (binary) states: ON/OFF High/Low One/Zero True/False Remember the transistor switch: Advantages of using digital circuits: Binary ones and zeros are easy to identify with an on or off state. 11

12 Logic Symbols and Functions AND Gate: Truth table: Inputs A B A B & C C Output C=H when A&B are H C=L otherwise A B C What is the function of a two input AND gate? Output is high only when both inputs are high 12

13 Digital Logic Building Blocks AND C = 1 when A&B = 1; 0 otherwise A B C NAND C = 1 when A&B=0; 0 otherwise (not AND) OR C=1 when A and/or B = 1 C =0 when A&B = 0 NOR C = 0 when A and/or B = 1 C = 1 when A&B = 0 13

14 Bits and Number of States One bit can be 1 or 0 2 states 2 bits can be 00, 01, 10, 11 4 states A byte is 8 bits and has 256 states In general the number of states of N number of bits is 2 N Example: How many states does a 3 bit counter have? 2 3 = 8 14

15 Other Digital Devices By combining multiple gates digital functions can be implemented. Important examples: Flip-flops two stable states that are stored and can be changed in various ways. Counters Flip-flops connected so that they count in binary every time they are clocked Shift registers Sequential flip-flips connected so that data can be transferred (or shifted) from one flip-flop to the next or alternately a clocked array of circuits that passes data in steps along the array. 15

16 High Level of Integration By higher levels of integration of gates very complex digital functions can be built on a chip. Examples: Microprocessors Microcontrollers DSP s (Digital Signal Processors) Complex digital circuitry can often be replaced by what type of integrated circuit? Microcontroller 16

17 Time vs. Frequency Domain Amplitude Amplitude Frequency = F Time Frequency = 10xF F Frequency 10F Sin (F 1 ) x Sin (F 2 ) = ½ [ sin (F 1 + F 2 ) + sin (F 1 F 2 )] 17

18 Radio Building Blocks These are the basic building blocks of most radios: Filters Oscillators Amplifiers Mixers Multipliers Modulation and modulators We will discuss each building block and then see how they can be put together. 18

19 Filters An ideal filter will pass one set of frequencies and blocks others. V IN Low Pass V OUT V V OUT IN 1 0 F cutoff Frequency Practical Low Pass Filter V V OUT IN 19

20 Filter Types Low Pass High Pass Band Pass Low pass filters are especially important for front end and out output of transceivers. Band pass filters are important in the intermediate frequency (IF) stages of receivers. The impedance of a low-pass filter compared to the impedance of the transmission line into which it is inserted should be about the same. 20

21 Oscillators An oscillator is a circuit which produces a waveform (often but not always a sine wave) at a fixed or variable frequency. Amplifier βv OUT Gain = A Filter: Feedback Fraction = β A β V OUT V OUT An oscillator consists of an amplifier with feedback from output to input. A filter is needed in the feedback to assure oscillation is only at one frequency What are the basic components of an nearly every Oscillator? A filter and amplifier operating in a feedback loop. 21

22 Oscillators Feedback (β) in an oscillator can be of various forms and configurations including L s and C s, crystals, and even light bulbs. Crystals are useful because they vibrate very accurately. LC circuits are often configured as resonant or tank circuits At the frequency where the tank circuit is at resonance 1 2πFC = 2πFL F = 2π LC The resonance will determine the frequency of the oscillator 1 What determines the frequency of an LC oscillator? The inductance and capacity of the tank circuit. 22

23 Tunable Oscillators Two other widely used tunable oscillators in radios are: Phase-locked loops (PLL) Direct Digital Synthesizer (DDS). DDS is a digital device that can be programmed by a computer or microprocessor to oscillate at a specific frequency and they can be very stable. They are used in a lot of ham applications. What is the advantage of a transceiver controller by a direct digital synthesizer? It has variable frequency with the stability of a crystal oscillator. 23

24 Amplifiers Amplifiers increase the strength (e.g amplitude) of signals. The term Linear Amplifier or linear is used usually to describe the equipment that amplifiers the output of a transmitter up as much as the legal limit 1500 watts Linear amplifiers operate so that the output preserves the input waveform. RF Power Output Amplifier efficiency = DC Power Input 24

25 Amplifier Linearity Linearity is a measure of how well the amplifier it preserves the input signal without creating signal distortion. In general amplifier linearity is inversely proportional to efficiency: Efficiency Linearity 25

26 Amplifier Efficiency Class A most linear, low distortion (output transistors always in active region) Class B efficiency good and linearity can be good (output transistors push-pull each operating during half cycle) Class AB Between A and B in operation Class C Very un-linear, but highest efficiency (output transistors are being switched off and on) Suitable only for CW 26

27 Amplifier Neutralization In vacuum tube linear amplifiers parasitic capacity can create enough positive feedback to cause oscillations. A solution is provide some addition negative feedback in the circuit to cancel the positive feedback. This is call neutralization and is implemented by connecting a small variable capacitor from output to input of the circuit to provide negative feedback. What is the reason for neutralizing the final stage of a transmitter? To eliminate self-oscillation. 27

28 Mixer The Mixer is a circuit that multiplies two signals which creates sum and difference frequencies. This mixing process is called heterodyning. The mathematical basis of mixing is the trigonometric property: sin( a) sin(b) = 1 [sin(a + b) + sin(a b)] 2 F 1 X F 1 + F 2 F 1 - F 2 In Radio circuits, F 1 is usually the RF input and F 2 the local oscillator F 2 Example To shift frequencies to a 455 Khz IF: F 1 = Mhz F 2 -F 1 = 455 Khz F 2 = Mhz F 2 +F 1 = Mhz Remove this frequency with a low pass filter. 28

29 Mixer Operation and Interference What receiver stage combines Mhz input signal with a MHz oscillator to produce a 455 khz intermediate frequency (IF) signal? --Mixer If a receiver mixes a Mhz VFO with a received signal to produce a 455 KhZ intermediate frequency (IF) signal, what type of interference will a Mhz signal produce in the receiver? --Mixer interference. ( =455 two input frequencies mix. 29

30 Multiplier A Multiplier circuit operates in a similar manner to a mixer but instead of creating sum and differences of the input, it creates harmonics of an input frequency. Multipliers are often used in VHF and UHF radios to create a higher frequency signal. What is the stage in a VHF FM transmitter that generates a harmonic of a lower frequency signal to reach the desired operating frequency? --Multiplier 30

31 Modulation Modulation is the process of adding information to an RF signal (i.e. the carrier) by varying frequency, amplitude or phase. Amplitude modulation: F Carrier X F Carrier + F Audio Upper Side Band (USB) F Carrier - F Audio Lower Side Band (LSB) F Audio 31

32 AM Modulation AM Amplitude Modulation: phone transmission in which the voice signal modulates the carrier. What type of modulation varies the instantaneous power level of the RF Signal? --Amplitude modulation What is the modulation envelope of an AM signal? --The waveform created by connected the peak values of the modulated signal Modulation envelope 32

33 SSB Modulation SSB Single Side Band, only one of the two sidebands is transmitted; one sideband and the carrier are suppressed What is the advantage of carrier suppression in a single sideband phone transmission versus full carrier amplitude modulation? --Available transmitter power can be used more effectively Which phone emission uses the narrowest bandwidth: -- Single sideband What control is typically adjusted for proper ALC setting on a signal sideband phone transmission. -- Transmitter audio or microphone gain 33

34 Modulation and Transmission Issues What is the effect of over modulation? --Excessive bandwidth With over-modulation the sidebands will start to extend and use more than the desired bandwidth. Amplifiers which are over-driven product an output that saturates or flat-tops and so produce a distorted output What is meant by the term flat-topping when referring to a single side band transmission? --Signal distortion caused by excess drive 34

35 Frequency Modulation FM frequency modulation, changes instantaneous frequency of RF to convey information To amplifier A A A reactance modulator F changes its reactance as a function of the signal that controls it. 35

36 Phase Modulation PM phase modulation, changes phase angle of the RF wave to convey information Phase Modulation FM modulated signal Oscillator Reactance Modulator PM modulated signal To amplifier AF AMP What emission is produced by a reactance modulator connected to the transmitter RF amplifier stage? --Phase Modulation 36

37 How Does a Receiver Work? A radio receiver need to 1. capture a signal 3. Detect or demodulate 2. provide gain and filtering 4. Drive a speaker or headphones. Tuned RF radio 37

38 The Superheterodyne Receiver RF Amp Mixer IF filter IF Amp Product Detector AF Amp Local Oscillator Beat Frequency Oscillator (BFO) The Superheterodyne Receives and amplifies the RF signal Mixes the RF signal to the IF frequency Processes and filters the signal in the IF section Amplifies the IF signal With the BFO and Product detector generates an audio signal Amplifies and outputs this audio signal and with a little luck you can hear New Zealand calling. 38

39 The Superheterodyne Receiver RF Amp Mixer IF filter IF Amp Product Detector AF Amp Local Oscillator Beat Frequency Oscillator (BFO) The function of the Mixer in a Superheterodyne is to shift frequencies from the RF frequency to an intermediate frequency (IF) for filtering and processing. Together with the Local Oscillator it generates the mixing products that are processed by the IF filter. 39

40 Product Detector and BFO RF Amp Mixer IF filter IF Amp Product Detector AF Amp Local Oscillator Beat Frequency Oscillator (BFO) A Product Detector is a type of mixer that allows a receiver to demodulate CW and SSB signals A Beat Frequency Oscillator (BFO) produces a sine wave which mixes in the product detector to demodulate the IF output and generate the received audio signal. Other detectors are used for AM (envelope detector) and FM (discriminator) 40

41 The Superheterodyne RF Amp Mixer IF filter IF Amp Product Detector AF Amp Local Oscillator Beat Frequency Oscillator (BFO) What circuit is used to process the RF signals from the RF amplifier and send them to the IF filter in a superheterodyne receiver? Mixer What circuit is used to combine signals from the IF amplifier and BFO and send the result to the AF amplifier in some single sideband receivers? Product Detector 41

42 The Simplest Superheterodyne RF Amp Mixer IF filter IF Amp Product Detector AF Amp Local Oscillator Beat Frequency Oscillator (BFO) The simplest combination of stages that implement a superheterodyne receiver are: HF oscillator (aka local oscillator) Mixer Product detector. 42

43 Digital Signal Processing DSP s are special purpose processors which do signal processing that once was done entirely by analog circuits. They are found in the IF section of most modern radios to do programmable band pass and notch filtering and in the audio section to do equalization and noise reduction. Many new radios called Software Defined Radios (SDR s) are almost completely based on DSP s and associated control IC s and most singal processing functions are performed by software. ADC DSP DAC Digital world Analog world 43

44 Digital Signal Processing How is Digital Signal Processing Accomplished? By converting the signal from analog to digital and then using digital processing. What is necessary for a Digital Signal Processor IF: ADC Analog to digital converter DAC Digital to analog converter Digital Processor chip 44

45 CW Transmitter The CW transmitter takes sine wave (constant waveform CW) mixes it to the transmission frequency, filters out harmonics, and sends it out through an amplifier that is turned on and off by a key hence creating dits and dahs. Variable Frequency Oscillator VFO Mixer Amplifier Filter Local Oscillator (LO) Key or Keyer 45

46 SSB Transmitter A SSB transmitter mixes an audio signal with a carrier sine wave in a balanced modulator, filters the output to eliminate one of the two side bands, mixes to a transmission frequency, filters the result to reduce harmonics, and provides amplification for transmission. Carrier VFO Balanced Modulator Filter Mixer Filter Amplifier Local Oscillator (LO) Speech Amp 46

47 SSB Transmitter What circuit is used to combine signals from the carrier oscillator and speech amplifier then send them to the filter in some single sideband phone transmitters? --Balanced Modulator What circuit is used to process signals from the balanced modulator then send them to the mixer in some single sideband phone transmitters? --Filter 47

48 VHF FM Transmitters Reactance Modulator Multiplier Filter Osc. RF Amp Speech Amp FM transmitter generally produce the FM signal at lower frequencies and then use a multiplier to move the signal to VHF frequencies. If we want a transmitter to operate on the 2 meter band and the multiplier is 12, then the oscillator must operate at Mhz/12 = Mhz. The frequency deviation of the FM is multiplied also by 12 in this example. If 5 khz deviation is desired at the output, then deviation of the reactance modulator must be 5kHz/12 = 416.7Hz 48

49 Digital Modes There is an ever increasing number of digital modes used in ham radio and and often in DX: RTTY important for contests and DX PSK31 useful for casual QSO s and occasional DX Pactor and Winmor more of a legacy mode JT65 and J9 great in bad band conditions, some DX --Operate at extremely low signal strength on HF bands FT8 brand new mode that is becoming important, DX 49

50 Bandwidths of Transmission Modes One of the advantages digital modes is that they often use very little bandwidth. Mode Bandwidth (HZ) PSK31 50 FT8 50 CW ~100 RTTY 200 MFSK JT PACTOR 2300 SSB 3000 FM (assuming 5KHz deviation and 3kHz modulating frequency It is good to match the receiver bandwidth to that of the operating mode? It results in the best signal to noise ratio. * * not necessary or desirable on many digital modes. 50

51 PSK31 PSK or Phase Shift Keying is a very low bandwidth mode that still performs well in bad conditions. It is computer generated and decoded (for example FLDIGI program) and the interface to the radio is a sound card. PSK coding scheme is varicode the number of bits being varies and depends on the specific letter Uppercase letters use more bits and slow transmission slightly The 31 in PSK stands for the transmitted symbol rate which is A good typist can out-type PSK transmission. Symbol rates is the rate at which individual data symbols are transmitted. Higher symbol rates require higher bandwidths. 51

52 RTTY RTTY transmission moves between two tones called mark and space. The difference between the two tones is called the shift. The most common shift is 170Hz FSK signal is generated by changing an oscillators frequency directly with a digital control signal. The modulation scheme is called Frequency shift keying (FSK). The underlying code is called Baudot code a 5 bit code with additional start and stop bits. RTTY has a very characteristic sound on the air that you will quickly identify 52

53 RTTY The RTTY code is generated and decoded in a computer (for example MMTTY program). There are two ways for the computer to talk to the radio: FSK -- the computer directly instructs the radio to shift back and forth between mark and space frequencies. AFSK -- a (sometime specialized) soundcard generates audio signals and they are transmitted on SSB or FM RTTY usually uses the LSB. Often if you can t decode a RTTY signal you (or your contact) may be on the other sideband. RTTY is a nearly 100% duty cycle mode when transmitting and care must be taken not to overload your amplifier. It is important to know the duty cycle of the mode so to not overload the amplifier. 53

54 Packet Modes Packet modes transmit data (packets) rather than bits and often include error detection and correction. Typical packet format (string of bits): Header Data Trailer Routing and handling information Status and error correction info Packet communication is only a two way protocol. If errors are detected in the received message, a new request for a new packet is made. If there are too many re-transmission requests, the connection is dropped 54

55 Packet Protocols PACTOR and WINMOR protocol messages: NAK response (not acknowledges) the receiver requests a re-transmission of information ARQ automatic repeat on request mode. If receiving station responds to ARQ data mode containing errors, it requests the packet to be re-transmitted FEC (Forward error correction) allows the receiver to correct errors in received data packets by transmitting redundant information with the data 55

56 Packet Pactor is a two way communication scheme so it is impossible to join an existing communication. Pactor bandwidth is 2300Hz 56

57 Thank you You should now be prepared to pass the General Class license test Subelements 7 and 8 57

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